1. Field of the Invention
This invention relates to a magnetic recording disk cartridge, and more particularly to a magnetic recording disk cartridge for a magnetic recording disk which is small in diameter and extremely thin in thickness and which is rotated at a high speed for recording or reproduction.
2. Description of the Prior Art
There has come into wide use as a recording medium for computers a floppy disk which is a flexible disk of polyester resin coated with magnetic material on both sides thereof and on which digital information is recorded by a magnetic head. The floppy disk is easy to handle and inexpensive.
Recently, there has been proposed a photographic still camera in which, instead of a conventional silver salt photographic film which cannot be reused, a magnetic recording disk smaller than the floppy disk both in thickness and diameter is used as a recording medium. This still camera is generally referred to as "an electronic camera". This electronic camera is generally about the size of a typical 35 mm photographic camera. In the electronic camera the image of an object is magnetically recorded on the magnetic recording disk while the disk is rotated at a high speed. Generally the magnetic recording disk for the electronic camera is accommodated in a hard casing to form a cartridge and is loaded in the camera body together with the casing.
The magnetic recording disk for the electronic camera comprises a recording medium which is small in diameter and is extremely thin, and a hub fixed to the center of the recording medium. The casing for the disk has a hub opening through which the hub is exposed and a pair of magnetic head receiving openings in the front and rear side walls thereof, the magnetic head receiving openings being provided to give the magnetic head of the recording-reproducing system access to the recording medium. In this specification, the term "recording-reproducing system" should be broadly interpreted to include systems for recording only and for reproduction only.
In recording images using a magnetic recording medium, signals are densely recorded on the magnetic recording medium since video signals have a wider frequency band than digital signals or audio signals. Accordingly, when fine unevenness, scratches or flaking exists in the magnetic coating on the magnetic recording medium or when dust is deposited on the magnetic coating, so-called drop-out occurs during reproduction and the recorded signals cannot be faithfully reproduced. Since the magnetic recording disk cartridge for the electronic camera is frequently used outside, dust is apt to get into the inside of the casing through the magnetic head receiving openings to adhere to the surface of the recording medium and there is a danger that the part of the recording medium exposed through the magnetic head receiving openings may be brought into contact with something outside the casing to be scratched thereby, while the cartridge is being carried.
Therefore, such cartridges are generally provided with a shutter member which normally closes the magnetic head receiving opening and opens when the cartridge is loaded in the recording-reproducing system. The shutter member is typically a flat member which is rotatably supported on an engaging portion formed at the center of the casing and is connected to a connecting member having an end portion exposed outside the casing, and is moved along the inner surface of the casing to open and close the magnetic head receiving opening in response to operation of the exposed end portion of the connecting member. Since the shutter member is generally stamped from, for instance, a steel plate, the shutter member inherently has a burr on one surface thereof along its peripheral edge. Therefore, when the shutter member is mounted with the surface bearing thereon the burr being directed toward the inner surface of the casing, it becomes hard to move the shutter member due to increased friction between the inner surface of the casing and the surface of the shutter member. This problem can be overcome by barreling the stamped shutter member, for example. However, since the shutter member is made extremely thin so as to be mountable in the flat casing, it is apt to be bent during barreling.